Sclerotherapy is a medical procedure used to eliminate varicose veins and spider veins. Sclerotherapy involves the near painless injections of a detergent or irritant, that causes small spider veins to collapse and no longer fill with blood.The solution irritates the lining of the blood vessel, causing it to swell and stick together, and the blood to clot. Over time, the vessel turns into scar tissue that fades from view. In the video below you can appreciate how the blood vessel blanches away when injected.